The 13 Labour years just past, and now receding fast, were a glorious era for builders. From London's Millennium Dome and Olympic zone, to northern England's "regenerated" city centres, to the windswept out-of-town tracts turned into transport hubs and hospitals, to the sheltered middle-class streets bursting with loft extensions, much of the UK spent 1997 to 2010 behind construction hoardings. A lot of public money was used; a lot of private money was borrowed. There had not been such an attempt to remodel tatty old Britain since the great postwar reconstruction of the 50s and 60s.

What was the result? It is a rarely asked but important question – especially important now, with the coalition's deep cuts and the cranes beginning to disappear from our skylines. For good or ill, the built environment the Blair and Brown governments created, directly and otherwise, is the one we're likely to be living in for quite a while.

At times its architecture and planning make Owen Hatherley despair. Near the end of this angry, melancholy book, he visits the former Dome, now the music venue the O2, and the surrounding Greenwich peninsula. Once, he writes, "this place was a Blairite tabula rasa . . . an area the size of a small town, freshly decontaminated and waiting to have all manner of ideas laid down upon it." But now, instead of the green, inclusive, continental-style new city quarter Labour supporters might have hoped for, he finds "a transplant of America at its worst – gated communities, entertainment hangars and malls criss-crossed by carbon-spewing roads; a vision of a [British] future alienated, blankly consumerist, class-ridden."

Elsewhere in Hatherley's addictive illustrated travelogue, we encounter "cramped speculative blocks marketed as 'luxury flats'", "pointless piazzas with attendant branches of Costa Coffee", the "Disneyfication" of museums, "class cleansing" disguised as urban regeneration, and, everywhere, a glass‑and-steel contemporary building style that he calls "Pseudomodernism": superficially like the old 20th-century modernism but "emptied of all intent to actually improve the living conditions of the majority".

Hatherley, who is a prolific architecture blogger, has a nice line in put-downs and sarcasm. Sometimes, in the age-old way of English polemicists, he doesn't let the facts get in the way of a good denunciation. That the Dome and much of the current landscape of the Greenwich peninsula were actually conceived by John Major's Conservative government, for example, and so never quite offered the Blair administration that followed a "tabula rasa", is mentioned only in passing.

Yet what elevates this book far above the usual leftist attacks on New Labour's questionable building projects and white elephants – many of these attacks, however acute, providing unintended but useful ammunition for the state-shrinking schemes of the coalition – is a sense of historical perspective and a sense of sadness. Hatherley is only 29, but his politics and aesthetic preferences are interestingly old-fashioned. In his previous book, Militant Modernism, an acclaimed 2009 essay collection, he wrote with fierceness and longing about the nearly lost worlds of 20s Soviet avant-garde architecture and the "brutalist" British buildings of the 50s and 60s that carried forward some of the ideas of these communist pioneers.

Hatherley comes from a radical leftwing family, and is loyal, sometimes startlingly so, to the old socialist dreams of salvation through concrete and collective living. But he is also young and astute enough to see that one of the best arguments for the "abhorred architecture" he loves is the shortcomings of what has been built since, the often shoddy and cruel cityscapes that have been erected across the world since the left went into possibly terminal retreat in the 80s. So in this book he undertakes a double search: for the Britain New Labour built, and for the more radical postwar landscape that this construction boom partially erased.

He starts in Southampton, that scattered, little-written-about city on the south coast. Hatherley grew up there, and quickly disarms anyone who suspects he is some sort of slumming middle-class aesthete, naively idealising council estates, by telling us that as a teenager he lived on one himself. "What I remember," he writes, "is ubiquitous casual violence." Out of this revelation he builds a characteristically clever argument: the estate in question was not some grey postwar fortress but an interwar garden suburb with a park and "workers' cottages". If life could be so bleak in such a bucolic setting, he suggests, then the problems of Britain's council estates can't simply be blamed on later, less bucolic styles of municipal architecture.

Hatherley finds remnants of the latter all over the city: "elegant" 70s towerblocks, an angular 1966 stack of flats near the station that he calls "a glorious concrete Cunard". He is intensely nostalgic for the time when British working-class housing was ambitious, even overbearing in design, rather than, as now, modest and seemingly ashamed of itself – when it is built at all. Yet his enthusiasm for this postwar architecture does not stop him noticing how beleaguered and desolate much of it has since become. The Southampton station block, he writes, "clearly hasn't been cleaned in a very long time . . . Adjacent is a small bombsite-cum-park, benches, rats and bristling vegetation."

Built around, beside, and in some cases on top of these worn buildings are the even larger edifices of the New Labour era. Hatherley lingers over Southampton's huge WestQuay mall, which opened in 2000: "shiny, plasticky cladding . . . walls thick enough to withstand a blast or a ram-raid . . . massive car parks . . . a spectacular incoherence to it all." His distaste is evident, but so is a kind of excitement. Like "some of the architecture I love", he writes, "it's out of scale, it's too monumental, it's fortress-like, it's Not In Keeping."

Unlike most polemics, this book is roomy and intellectually sophisticated enough to permit such moments of ambivalence. And Hatherley is also perceptive enough to spot the common ground, rarely acknowledged, between the postwar Britain of over-optimistic council estate construction and the post-Thatcher Britain of over-optimistic building for consumption. He even finds some contemporary structures he approves of: a cluster of "charming", "futuristic" eco-houses in Milton Keynes, and the aerial walkways of the new Merseyside mall Liverpool One, "swooping across each other, a Piranesian spectacle in pink and green".

Yet as he noses around his dozen chosen cities in England, Wales and Scotland (he has little interest here in non-urban Britain), Hatherley's tone grows progressively more disillusioned. Manchester riles him in particular. With a buffed-up city centre dominated by a new Selfridges and Harvey Nichols, and a huge, half-finished housing development called New Islington, Manchester was probably the archetypal New Labour boomtown. Hatherley acidly contrasts it with the rundown but culturally vibrant Manchester of the late 70s: "Regenerated cities produce no more great pop music, great films or great art than they do industrial product. What they do produce is property developers."

In one of the book's many counter-intuitive but revelatory sections, he attempts to rescue the reputation of Manchester's most notorious 70s estate, the now-demolished Hulme Crescents. "A series of labyrinthine blocks accessed by street decks", the crescents took barely half a dozen years from completion to become a local byword for crime and alienation. Yet, writes Hatherley, "all the things bemoaned as deleterious to family life . . . the complexity of the blocks, the noise and sense of height, the lack of a feeling of 'ownership' in the communal areas" turned out to be "perfect" for a different sort of tenant, Manchester's young bohemians, who relished the estate's air of decaying modernism. By the early 80s, it had an arthouse cinema, club nights run by the soon-to-be-famous Factory Records, and even a "Hulme look" of intense youths in baggy secondhand suits. On the estate and in the city generally then, writes Hatherley, "the very fact that [many] spaces were unused . . . led to a sense of possibility absent from the sewn-up, high-rent city of today".

You can criticise this view as too romantic. Britain's cities now probably are blander than in the postwar decades, yet for the majority of their inhabitants they may also work better. Central London, for example, with its new pedestrianised sections and cycle lanes, its expanding and ever more popular museums and galleries, its recently acquired confidence about how to use public spaces, is not somewhere Hatherley covers. Nor does he write about some of the grim modern places – airports, call centres – that might have provided his critique of New Labour with some of its best evidence.

But this is a personal, crusading book – not an encyclopedia or a thinktank paper. Like one of the postwar megastructures Hatherley cherishes, it may be a bit jerry-built in places, but it is bold and original, and it may change how you see British cities.

Andy Beckett's When the Lights Went Out: Britain in the Seventies is published by Faber.